The advent of the AIDS virus requires that structures of the greatest safety be employed for hypodermic needle syringes. While blood extraction for diagnosis is an important area of hypodermic needle contamination, a much more frequent use of hypodermic needles occurs in the injection of medicine, anesthesia and various liquids. Once an injection is made and the needle withdrawn from the patient, the needle tip is contaminated with the microorganisms of the patient. Thereafter any accidental pricking of other persons by the needle will transfer to that person such microorganisms. Various removable sheaths have been devised to cover the needle both before and after use. However manually placing the sheath over the needle exposes the operator to accidental pricks of the needle. Various sliding sheaths have been devised that remain mechanically connected to the syringe at all times. Usually these sheaths are spring biased to cover the needle. However if the sheath contacts a person it will retreat and slide until the needle penetrates that person, passing on the contamination. The contamination is injected under the skin, an area where it cannot be easily removed and where the contamination is most likely to spread.